This invention relates to waveguide pressure windows and more particularly to windows providing low loss, wide band microwave transmission through a high pressure seal.
Waveguide pressure seals are commonly employed in microwave systems and related devices to provide for different pressures in different waveguide sections and to assure that either water or air is precluded from entering the inside of the guide. Usually, the waveguide window is placed in a location where it is convenient to disconnect or connect the various components or at places where the guide traverses a barrier separating one environment from another. The purpose of creating high pressure waveguide structures is to maintain relatively constant conditions in the waveguide itself irrespective of the change in environment, temperature, ambient humidity, and the presence or absence of water.
When waveguide pressurization is not maintained, there is a tendency to encounter problems regarding Rf conduction and changing impedance. Moreover, condensation has a tendency to form in an unpressurized and unsealed waveguide which creates the deleterious condition of arcing and shorting. High pressure waveguides overcome this problem and if the seals are appropriately maintained, the inside of the waveguide may be filled with a dielectric gas to preclude moisture and when raised to positive pressure levels, improve power handling capability. The capability to withstand high pressure is not easily acquired and maintaining a low insertion loss over band width ratioed at 2.4:1 is difficult to attain. For example, Trousdale U.S. Pat. No. 3,001,160 discloses a high pressure waveguide window employing a dielectric plug having a transitional length equal to .lambda./4 and an overall plug length equal to .lambda./2. The plug material suggested by Trousdale includes teflon and polystyrene. This design and the materials employed are characteristic of a structure for narrow band width performance and gives no consideration to problems relating to high levels of hydrostatic pressures contemplated by this invention. Consonant with considerations as used above, the need arises to effectively provide a watertight seal in combination with a microwave window where the waveguide traverses a barrier as for example when an antenna, enclosed within a sealed radome, enters through the bulkhead of a submarine or the like to a microwave receiver. It is essential that sea pressure is prevented from entering the submarine in the event that the radome seal integrity is compromised.